This study will begin a re-examination of the psychobiology of N,N- dimethyltryptamine, an endogenous hallucinogen. Careful recruitment of experienced hallucinogen users will precede the development of a DMT rating scale, developed by administration of a high dose of DMT to 10 subjects. Lower doses will be administered to develop dose-response curves to the neuroendocrine effects of this compound and to validate the DMT rating scale.